1. Field of the Invention
The present invention relates generally to rotating optical media players, and specifically, to a method and apparatus which simplifies the requirements for implementing a pause function on a rotating optical media player.
2. Background of the Invention
A pause function is typically initiated when a user presses a pause button on a media player. In response, the media player stops its current activity and waits until the pause function ends. When the pause function ends, the media player usually resumes its prior activity at the same place it was when the pause function was initiated. Current techniques for pausing a rotating optical media player are complicated and require precise and expensive circuitry to implement the pause functionality. The precision and expense of such circuitry make it disadvantageous to implement pause functionality using current techniques. Before further discussing this problem, and overview of rotating optical media players is provided.
Rotating Optical Media Players
A rotating optical media player can be either a device or system that is capable of retrieving information stored by an optical disc, or a device or system that is capable of both recording information to and retrieving information from an optical disc. Examples of devices that are capable of retrieving information from an optical disc include compact disc (CD) players, video laser disc (LD) players, digital video disc (DVD) players, and compact disc read-only-memory (CD-Rom) drives. Examples of devices that are capable of both recording information to an optical disc and retrieving information from an optical disc include recordable mini-disc (MD) players, magneto-optical (MO) disc drives and compact disc recordable (CD-R) drives.
Information is generally stored by an optical disc in the form of concentric or spiral tracks sometimes referred to as information tracks. In the case where information is already stored by an optical disc, the information tracks contain regions of optical contrast that represent the stored information. In the case of an unrecorded or blank optical disc containing preformatted tracks for recording information, a track that will become an information track may or may not have regions of optical contrast. The area located between two information tracks on an optical disc is sometimes referred to as a non-information track.
When an optical storage device is in its normal mode of operation, (i.e. retrieving information from or recording information to an optical disc), the storage device rotates the disc while using a light beam to retrieve information from or record information to the disc. As the optical disc rotates, the light beam radially traverses the disc. While the light beam traverses the optical disc, a tracking servo loop in the optical disc storage device keeps the beam of light centered on the information track, or the track that will become the information track in the case of recording information to a disc.
Tracking Servo
An optical disc tracking servo is a closed loop system that allows a light beam to remain centered on an optical disc information track during normal operation of an optical disc storage device. The tracking servo readjusts the radial position of the light beam by sensing when the light beam drifts off the center of the information track. The tracking servo senses when the light beam is not centered on an information track by measuring the intensity of light reflected by the surface of the optical disc.
Generally, the intensity of light reflected by the surface of an optical disc is the least when it is reflected by the center of an information track. Using this principle, a tracking servo generally senses the intensity of light reflected at one or both edges of an information track to detect when a light beam is drifting off center and to determine in which direction the light beam is drifting. Therefore, a tracking servo system that is in a closed loop mode of operation senses when the light beam floats off the center of the information track by detecting changes in the intensity of light reflected at one or both edges of an information track and moves the beam back into a position where the intensity of reflected light is optimal for center tracking.
In the case where a tracking servo measures the intensity of light reflected at both edges of an information track, the intensity of reflected light that is optimal for center tracking occurs when the intensity of light reflected at both edges of an information track is the same. The same principle holds true for both one and three beam optical disc storage devices. In the case where a tracking servo measures the intensity of light reflected at one edge of an information track, the intensity of reflected light that is optimal for center tracking is based on some calibrated value. The latter method is less favored due to difficulties associated with calibrating an appropriate centering value.
Special Operations
Rotating optical disc media players are generally capable of performing various special operations in response to user input. One such operation is a pause, or still mode operation. Using current techniques, a pause operation is implemented in a manner that is illustrated in FIG. 1. Spiral track 100 of rotating optical medium 101 has a current position 110. The current position is where the laser was located on the spiral track 100 when the pause operation was initiated. The tracking servo remains closed after the pause operation is initiated by the user. Since the tracking servo loop remains closed at this point, the laser continues to spiral around the information track even after the pause operation starts.
When the loop reaches a second point 120, a full track has been cycled through spiral track 100. The second point 120 and the current position 110 are related by a radial line 121 drawn from the center of the medium 101 to its outside edge. Once the second point 120 is reached, the tracking servo loop is briefly opened and special circuitry causes the optical pickup controlling the laser to jump back to position 110, at which time the tracking servo loop is again closed. At this point, the laser continues to spiral to point 120 again and jump back to point 110 until the pause operation terminates.
Causing the optical pickup to jump between points 120 and 110 requires a great deal of precision. Typically the distance between tracks is 2 micrometers, so the jump is across a very small distance. To jump such a small distance, special jump circuitry is needed. Furthermore, the spiral pattern on a rotating disc is not perfect, so even a perfect 2 micrometer jump might not bring the laser to the correct location. Typically with such a small jump, the optical pickup has a tendency to jump to far (i.e., across more than one track), so zero crossing circuitry and break circuitry must also be used in conjunction with the jump circuitry, to sense when the laser has jumped halfway between the two tracks and to keep the pickup from moving too far (i.e., centering it on the next track). As a whole, the pause operation performed in this manner is complex and requires very expensive and precise equipment.
The use of such expensive and precise equipment is disadvantageous. The disadvantage becomes even more problematic and wasteful in media player applications that do not require absolute precision. For instance, when a pause operation is implemented by a user of a CD player who is listening to a song, it might be tolerable to emerge from the pause state at a location on the track that is not precisely where the pause operation was started. Instead, a location that is reasonably close to where the pause operation was started is tolerable. The end result might be a very small gap in the song of one or two notes that would be unnoticeable to the listener. Implementing a pause operation with expensive and complex circuitry in this application is wasteful and unnecessary.